March 2, 191 1] 



NATURE 



literature of this new and fascinating field of scientific 

 inquiry, and redounds to the credit of Mme. Curie, and 

 to the nation which has taken such a fundamental and 

 prominent part in the development of radioactivity. 



E. R. 



DYNAMO-ELECTRIC MACHINERY. 



The Dvnamo: Its Theory, Design, and Manufacture. 



By C. C. Hawkins and F. Wallis. Fifth edition. 



Re-written, revised, and enlarged. Vol i., pp. x + 



I 542. Vol. ii., pp. viii + 543-1 134. (London : Whit- 



I taker and Co., 1909.) Price 21s. net, two vols. 



THE increase in the size of Messrs. Hawkins and 

 Wallis 's book is a good indication of the pro- 

 gress that has taken place in the practical development 

 of the dynamo. Little or no addition has been made 

 in the interval to the fundamental theory of direct- 

 current and alternating machines ; an immense ad- 



' vance has been made in the mastery of the thousand 

 and one details of selection of materials and methods 

 of construction of machines for different purposes. 



Vol. i. is mainly theoretical, and contains statements 

 regarding the physical facts and theories on which 

 electric generators and motors are based. The treat- 

 ment of the magnetic circuit, of self-induction and 

 alternating currents, the classification of dynamos, 

 the magnetic properties of iron, and so forth, strike 

 one as exceedingly satisfactory. In general there is 

 a clear perception of what constitutes a proof of a 

 theorem and what a mere illustration or representa- 

 tion of results. It is possible to frame graphical 

 proofs of theorems of electromagnetism, as of dynam- 

 ical theorems regarding stresses in the members of a 

 girder, and it is a good thing to do so ; but many so- 

 called graphical "proofs" are mere illustrations of 

 results which have been so far only satisfactorily 

 established by analysis. The graphical representation 

 displays to the eye connections of things set forth in 

 equations, and so far as possible this should be done 

 in all departments of mathematical physics; but the 

 student should not be led to imagine that he has got 

 to the roo t of the matter, when he realises that 

 V'R^ + n^'L^ is the length of the hypotenuse of a right- 

 angled triangle, the lengths of the sides of which are 

 R and nL. As it seems to us, Messrs. Hawkins and 

 Wallis have given a very happily blended analytical 

 and geometrical discussion. 



The analogy of inductance and capacity to inertia 

 and the slackness of a buffer spring, of the electro- 

 kinetic energy |Li^ to the kinetic energy of a carriage, 

 and the analogy of the dissipation of this kinetic 

 energy, when the carriage is brought to rest by 

 collision with the buffers, to the break of a circuit con- 

 taining a condenser, gives a clearer idea of what 



: happens than general statements, and we should have 

 liked to see some such practical "engineering" illus- 

 trations in the chapter on self-induction. 



Then it is a little difficult to distinguish, as the 

 authors seem to do on p. 69, between "the current 

 itself," and the magnetic field which it produces. Is 

 It not all one phenomenon? One mav try to distin- 

 i;uish between the current — the motion of electrons (or, 

 as someone has illuminatingly called them, the essen- 



\ tial singularities that are at the root of all electrical 

 NO. 2157, VOL. 86^ 



action) — and the magnetic field, but is it possible to 

 do so really? One cannot have a vortex filament in 

 an infinite fluid without the irrotational flow which 

 constitutes its field. It may be said that by twisting 

 the outward and inward wires of a circuit together 

 or by putting one inside the other, a field can be 

 avoided ; but the assertion is only true for space ex- 

 ternal to the conductors. A field can only be avoided 

 altogether by making the going and returning con- 

 ductors absolutely coincident, in which case there is 

 no current. 



The molecular theory of magnetism may possibly 

 require modification in view of still more modern 

 theories of the electrical constitution of matter; but 

 it has done much service in clarifying the ideas of 

 students of magnetism, and it still substantially 

 fits the facts. How often did one find in elementary 

 books the higgledy-piggledy arrangement of mole- 

 cular magnets pictured, to explain to the reader the 

 constitution of a body in the neutral state? It never 

 seemed to occur to the writers that these magnetic 

 molecules must act on one another, and that the per- 

 fectly fortuitous arrangement was unlikely to have 

 been set up, or to remain if it were. The closed 

 chains were in the minds of many ; the exhibition of 

 E wing's model made clear how these closed chains 

 led to the observed magnetisation curves. 



During the last year or two much further work on 

 magnetic induction in iron and alloys has been done, 

 and on the influence of treatment of different kinds : 

 it will be for the dynamo builder and user to examine 

 whether any part of the work is likely to be of use 

 to them. But no doubt for a long time the know- 

 ledge that has been accumulated of the constants of 

 steel of different kinds, in stampings of different thick- 

 nesses, will be sufficient for their needs. 



Chapters xiv. and xv. of the first volume, on " Field- 

 Magnets " and "The Ampere-Turns of the Field" 

 respectively, are exceedingly instructive and interest- 

 ing, and are, of course, of great importance, for the 

 proper design of a dynamo or motor for a given speci- 

 fied purpose depends entirely on a due appreciation 

 of the principles laid down in every sound discussion 

 of this subject. 



In vol. ii., after a discussion of armature reaction 

 which seems adequate, a long chapter (no pages) is 

 given on "Commutation and Sparking at the 

 Brushes." This important subject is very fully dealt 

 with, apparently with a thorough appreciation of all 

 that has been done on the subject of commutation and 

 the factors on which sparking at the brushes depends, 

 and also of the quantitative laws of the matter so far 

 as these have been theoretically and empirically com- 

 piled. 



Chapters follow on the "Design of Continuous- 

 Current Dvnamos and Alternators," and these are 

 based on a full description of all the various forms of 

 armatures and field-magnets in use in the various 

 types. 



The book, if a little heavy (in avoirdupois), is beau- 

 tifully printed and magnificently illustrated with 594 

 pictures, diagrams, and cuts of different sorts, and 

 reflects credit on authors and publishers alike. 



A. G. 



